The present invention is related to disc drive data storage systems and, more particularly, to a method of controlling curvature of a transducing head, such as a hydrodynamic bearing slider.
A typical hard disc drive includes one or more rigid discs coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective head gimbal assemblies (HGAs). Head gimbal assemblies carry transducers which write information to and read information from the disc surface. An actuator mechanism moves the head gimbal assemblies from track to track across the surfaces of the discs under control of electronic circuitry.
The head gimbal assembly includes a gimbal (or flexure) and a slider. The gimbal provides a resilient connection that allows the slider to pitch and roll while following the topography of the disc. The slider includes a slider body having a bearing surface, such as an air bearing surface, which faces the disc surface. As the disc rotates, the air pressure between the disc and the air bearing surface increases, which creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface. The transducer is typically mounted at or near the trailing edge of the slider
In some applications, the slider flies in close proximity to the surface of the disc. This type of slider is known as a xe2x80x9cpseudo-contactxe2x80x9d slider, since the bearing surface of the slider can occasionally contact the surface roughness of the disc. In other applications, the slider is designed to remain in direct contact with the disc surface with substantially no air bearing. These sliders are referred to as xe2x80x9ccontact recordingxe2x80x9d sliders.
It is often desirable to fabricate a slider such that the bearing surface has a positive curvature along the length and width of the slider. Length curvature is known as crown curvature. Width curvature is known as cross or camber curvature. The proper setting and control of crown and cross curvature improves fly height variability over varying conditions, improves wear on the slider and the disc surface, and improves takeoff performance by reducing stiction between the slider and the disc surface. In addition, the slider preferably has no twist about its longitudinal or transverse axes. While twist does not directly effect fly height, high twist values, either positive or negative, can cause other negative tribological effects, such as increasing wear and inducing roll.
Curvature has been controlled in the past by lapping the bearing surface on a spherically-shaped lapping surface or on a flat lapping surface while rocking the slider body back and forth in the direction of the desired curvature. The amount of curvature is determined by the radius of the rocking rotation. This lapping process is difficult to control and results in large manufacturing tolerances.
U.S. Pat. No. 5,442,850 discloses a method of controlling crown and cross curvature by inducing a preselected amount of compressive stress within a selected section of the bearing surface by impinging the section with particles for a preselected amount of time. U.S. Pat. No. 5,266,769 discloses a process of controlling slider crown and cross curvature in which the air bearing surfaces are first patterned and then a chosen pattern of stress is produced on the back side of the slider by laser oblation or sand blasting to selectively remove stressed material and thereby create a desired crown and cross curvature of the bearing surface.
U.S. Pat. No. 5,982,583 discloses a method of effecting slider curvature through the application of laser-induced anisotropic tensile stress, which allows one of the crown and cross curvature to be changed to a greater extent than the other curvature. In addition, Seagate Technology, Inc. has used a process of creating scratches on the back side of the slider (the side opposite to the air bearing), lapping the bearing surface flat and then laser heat treating the scratches to reduce compressive stress caused by the scratches and thereby cause a positive curvature change in the bearing surface. This process is discussed in U.S. application Ser. No. 08/662,849, Filed Jun. 12, 1996.
While the above techniques can be used to adjust slider curvature, improved methods are desired for selecting a particular curvature treatment on a slider-by-slider basis given incoming curvature values, such as crown, cross and twist curvatures, and predetermined curvature responses.
One embodiment of the present invention is directed to an apparatus for adjusting curvature of a disc head slider having a bearing surface. The apparatus includes a light source and an apparatus for controlling the light source. The light source is adapted to produce a light beam capable of altering material stresses in a working surface of the slider. The apparatus for controlling the light source is adapted for: (a) obtaining measures of first and second curvature characteristics of the bearing surface; (b) selecting a first material stress pattern to be applied to a working surface of the slider based on the measure of the first curvature characteristic and a first target value; (c) estimating a change to the second curvature characteristic due to application of the first material stress pattern to the working surface of the slider; (d) selectively changing the first target value and the first material stress pattern based on the change to the second curvature characteristic estimated in step (c); and (e) applying the first material stress pattern, as selectively changed in step (d), to the working surface of the slider to induce a change in the first curvature characteristic toward the first target value.
Another embodiment of the present invention is directed to an apparatus for controlling curvature of a disc head slider having a bearing surface. The apparatus includes a light source adapted to produce a light beam capable of altering material stresses in a working surface of the slider and includes an apparatus for (a) defining a respective specification range, including a nominal value, for twist, crown and cross curvatures of the bearing surface; (b) obtaining a measure of the twist, crown and cross curvatures of the bearing surface; (c) selectively altering material stresses on a working surface of the slider in a first pattern that is selected to induce a desired change in the twist curvature based on the measure of the twist curvature, the specification range for the twist curvature and estimated responses in the crown and cross curvatures to the first pattern; and (d) selectively altering material stresses on the working surface in a second pattern that is selected to induce a change in at least one of the crown and cross curvatures based on the specification ranges for the crown and cross curvatures and estimated responses in the crown and cross curvatures to the second pattern.
Another embodiment of the present invention is directed to an apparatus for controlling curvature of a disc head slider having a bearing surface. The apparatus includes a light source adapted to produce a light beam capable of altering material stresses in a working surface of the slider and an apparatus for (a) obtaining a measure of twist, crown and cross curvatures of the bearing surface; (b) selecting a first material stress pattern for inducing a change in the twist curvature in response to application of the first material stress pattern to a working surface of the slider, based on the measure of the twist curvature obtained in step (a); (c) estimating a response in at least one of the crown and cross curvatures to the first material stress pattern due to application of the first material stress pattern to the working surface of the slider; (d) selectively applying or not applying the first material stress pattern to the working surface of the slider, based on the estimated response in at least one of the crown and cross curvatures; (e) selecting a second material stress pattern for inducing a change in at least one of the crown and cross curvatures in response to application of the second material stress pattern to the working surface of the slider; and (f) applying the second material stress pattern to the working surface of the slider.